A must for aircraft developers, a luxury for athletes
by Hendrik Thielemann
Whether the goal is to improve performance, fuel efficiency or comfort, wind tunnels are an indispensable tool for aircraft and automotive development. And for top athletes, wind tunnel testing can put them in a class of their own.
The disappointment was huge when Wilbur and Orville Wright returned from Kitty Hawk, North Carolina, to their home in Dayton, Ohio, in 1901. The flight tests for their Glider No. 2 had been a disaster, shaking their confidence badly. Having started out with faith in existing scientific data, they began to doubt one thing after another. Finally, the brothers decided to cast it all aside and rely upon their own investigations.
The brothers decided they needed a wind tunnel and went about building a simple model. The preliminary results from the makeshift tunnel were so encouraging that they built a second facility. In this larger and more sophisticated tunnel, Wilbur and Orville Wright obtained the critical data they urgently needed to build the world’s first manned, powered aircraft capable of controlled flight.
The Wright brothers episode shows how integral wind tunnel testing has been to aircraft development since the early days of aviation. This relationship remains the same today. Whether the objective is to improve performance or to make an aircraft more economical or more comfortable, wind tunnel testing makes it possible.
During the development of a typical business jet, leading manufacturers will test several scale models for thousands of hours in various wind tunnels. Swiss manufacturer Pilatus Aircraft tested its new PC-24 business jet in the Czech Republic and the Netherlands, among other places – and also on its own doorstep in Emmen, Switzerland, where the technology group RUAG operates two wind tunnels.
Energy lasers and multiple cameras detailing airflow measurements around aircraft.
Each wind tunnel has its own niche
Why do aircraft manufacturers travel around the world testing their models in various facilities? Why does RUAG operate two different wind tunnels in Emmen? “Anyone who develops an aircraft will always carry out experiments in different wind tunnels to investigate different questions. There is no wind tunnel that can cover all needs. Each tunnel has its own niche,” explains aerodynamic engineer Daniel Steiling. Daniel and 30 colleagues make up the aerodynamics department at RUAG Aviation and are responsible for wind tunnel testing. In the Large Wind Tunnel Emmen (LWTE), the bigger of the two facilities, engineers focus on tests for the aviation industry. All major western aircraft manufacturers have run test campaigns in the LWTE.
Wind tunnel tests are usually conducted with scale models. The Large Wind Tunnel Emmen can accommodate models with a wingspan of up to five meters, making it one of the largest facilities in Europe, with a cross section of seven by five meters. The LWTE is particularly suitable for testing aircraft landing, take-off and maneuvering configurations. Another specialty is the testing of aircraft with propellers. Daniel and his team support customers throughout the entire test campaign – from the design of wind tunnel models to the manufacturing of models by subcontractors, to instrumentation, to the actual tests, and even to the evaluation of the data produced.
“You can quickly generate some impressive- looking and colorful pictures, but you need a deep understanding of your trade to produce results you can actually rely on.”
Motorsport investigations carry a special fascination as the results of modifications are seen in the next racing season.
Aerodynamic engineers believe wind tunnels will remain an indispensable tool for aircraft development in the future. This is because there is no one optimal and universally applicable aerodynamic form for an aircraft. “The optimum shape for an aircraft depends on the application,” says Daniel. Big airlines, for example, want to get as many people from A to B as cost- effectively as possible. “An airliner that flies a little slower and uses less fuel maybe fits the purpose better.” On the other hand, speed and comfort often play a more important role in business aviation. “Many travelers want to fly fast and save time, even if the costs are higher. They also want to feel comfortable and enjoy a quiet flight.”
It is believed that digitization will also have little effect on wind tunnel testing in the foreseeable future despite the gigantic advances in computing power. Aerodynamic engineers seem to be in agreement that it will not be possible to replace wind tunnel tests with computer simulations any time soon. “The equations governing the flow of air and any fluids are extremely complex,” remarks Daniel. He also explained that wind tunnels themselves are excellent simulation tools that allow a large amount of relevant data to be reliably generated in a relatively short time period. The computer simulations available today can provide a good approximation in some cases, but it is difficult to get it right. “You can quickly generate some impressive-looking and colorful pictures, but you need a deep understanding of your trade to produce results you can actually rely on,” says Daniel. “Simulations are often calibrated with the help of wind tunnel test results. Computer simulations and wind tunnels are two tools that supplement each other.”
The finishing touch for racing cars and top athletes
The automotive industry has been relying on wind tunnels to optimize aerodynamics and thus the performance of its cars for almost as long as the aviation industry has. Accordingly, RUAG reserves its second, smaller wind tunnel mainly for automotive customers. Daniel clarifies: “For the most part these are not big car manufacturers, but racing teams who carry out tests with us in order to further improve their vehicles.”
Last but not least, top athletes also use the wind tunnels in Emmen. This includes ski jumpers, downhill skiers, cyclists and even bobsledders – all looking to get the most out of themselves, their team and their equipment. Wind tunnel tests can certainly put athletes in a class of their own: “The posture, the material, whether the saddle of the road bike is one centimeter higher or lower – these things can make a huge difference,” says aerodynamics expert Daniel. However, wind tunnel testing is a luxury that only a few top athletes can afford. For these professionals, the tests are the icing on the cake, which can make the crucial difference between winning a medal and just missing the podium.
Experienced technical experts from different fields – performance, stability, control, icing, instrumentation and data processing – ensure the best possible design. (Photo: Dassault Aviation)